Abstract: 17-4PH(0Cr17Ni4Cu4Nb) steel is a martensitic precipitation strengthening stainless steel with high strength,good toughness and preferable corrosion resistance. During the inspection, it was found that there was red-brown suspected corrosion at the laser inscription of the installed 17-4PH hexagonal head bolt. The results show that the corrosion phenomenon of the fault bolt is mainly concentrated at the laser inscription, and the corrosion product is iron oxide with mud pattern. By comparing and analyzing new bolts and fault bolts, it is found that the fault bolt inscription shows a smooth melting characteristic morphology, while the other new bolt inscription shows the same rough morphology as the normal passivation surface. The microstructure characteristics of new bolt and fault bolt are consistent: the matrix is normal lath martensite, and there is a white bright layer at the laser inscription of the bolt. It was found by EBSD characterization that a small number of areas in the white layer of the bolt inscription transform into austenite, and extremely fine equiaxed grains were formed.Through simulation experiments, the macro/micro morphology and chemical composition of the two manufacturing processes bolts(laser inscription before surface treatment, and surface treatment before laser inscription) were compared. It is found that the surface morphology of the test bolts with surface treatment before laser inscription is consistent with that of the fault bolts,and there are similar attachments containing corrosive elements. It can be verified that the fault bolt is indeed due to the fact that the actual manufacturing process does not conform to the standard process, the surface is passivated first and then laser inscription leads to corrosion on the surface.